I just had an issue where users were directly added to the ACL of a folder. I created a group, added them to the group, added the group to the ACL of the folder and then removed the users and pressed apply. 18 of about 20 users were unaffected, but for some reason two users were denied access. I check the effective permissions tab and they were there. I added both users explicitly again.
i just did a fresh install of ubuntu 12.04 - 32 bit on my vps.
then i created a new user and added it into "sudo" group to allow sudo permission. then i tried to sudo to see whether it works or not. then i got "sudo: must be setuid root" warning. after googling for sometime i found out that /urs/bin/sudo file must be given chmod +s permission to make sudo work.